President Barack Obama talks about national security at the National Defense University at Fort McNair in Washington last week. The president left plenty of ambiguity in new policy guidelines that he says will restrict how and when the U.S. can launch targeted drone strikes, leaving himself vast power over how and when the weapons can be deployed.

WASHINGTON — President Barack Obama left plenty of ambiguity in new policy guidelines that he says will restrict how and when the U.S. can launch targeted drone strikes, leaving himself significant power over how and when the weapons can be deployed.

National security experts say it’s imperative to leave some room in the guidelines, given the evolving fight against terrorism. But civil rights advocates argue too little has been revealed about the program to ensure its legality, even as the president takes steps to remove some of the secrecy.

“Obama said that there would be more limits on targeted killings, a step in the right direction,” said Kenneth Roth, executive director at Human Rights Watch. “But a mere promise that the U.S. will work within established guidelines that remain secret provides little confidence that the U.S. is complying with international law.”

An unclassified version of the newly-established drone guidelines was made public Thursday in conjunction with Obama’s wide-ranging address on U.S. counterterrorism policies. Congress’ Intelligence committees and the Capitol Hill leadership have been briefed on the more detailed, classified policies, but because those documents are secret, there’s no way to know how much more clarity they provide.

The president has already been using some of the guidelines to determine when to launch drone strikes, administration officials said. Codifying the strictest standards, they argue, will ultimately reduce the number of approved attacks.

Among the newly public rules is a preference for capturing suspects instead of killing them, which gives the U.S. an opportunity to gather intelligence and disrupt terrorist plots. The guidelines also state that a target must pose a continuing and imminent threat to the U.S.

However, the public guidelines don’t spell out how the U.S. determines whether capture is feasible, nor does it define what constitutes an imminent threat.

Former State Department official James Andrew Lewis said Obama must retain some flexibility, given the fluid threats facing the U.S.

“The use of force and engagement of force always require a degree of discretion,” said Lewis, now a senior fellow at the Center for Strategic and International Studies. “We don’t want to change that.”

The guidelines also mandate that the U.S. have “near certainty” that no civilians will be killed in a strike. Civilian deaths, particularly in Pakistan, have angered local populations and contributed to a rise in anti-American sentiments in the volatile region.

Shahzad Akbar, a Pakistani lawyer who has filed many court cases on behalf of drone victims’ families, said that while he appreciated Obama’s concern about civilian casualties, he wasn’t confident the new guidelines would change U.S. actions.

“The problem remains the same because there is no transparency and accountability for the CIA because it will remain inside the system and not be visible to outsiders,” he said.

Obama, in his most expansive discussion of the drone program, said in his speech Thursday to the National Defense University that he is haunted by the unintentional deaths. But he argued that targeted strikes result in fewer civilian deaths than indiscriminate bombing campaigns.

“By narrowly targeting our action against those who want to kill us, and not the people they hide among, we are choosing the course of action least likely to result in the loss of innocent life,” Obama said.

Administration officials said the new guidelines are applicable regardless of whether the target is a foreigner or U.S. citizen.

Polling suggests the American people broadly support the use of drones to target suspected terrorists in foreign countries, though support drops somewhat if the suspect is a U.S. citizen. A Gallup poll in March found 65 percent of Americans favor using drone strikes in other countries against suspected terrorists, while only 41 percent favored the use of drone strikes overseas against U.S. citizens who are suspected terrorists.

Despite the public support, Obama has come under increased pressure from an unusual coalition of members of Congress of both parties who have pressed for greater transparency and oversight of the drone program.

Sen. Mark Udall, D-Colo., who serves on the Senate Armed Services and Intelligence committees, said he would review the guidelines to ensure they agree “with our values as a nation” but indicated lawmakers may ask for additional overtures.

“I commend the president for his effort to define the boundaries of U.S. counterterrorism operations and for stating a commitment to increased accountability,” Udall said. “While this is helpful and important, more needs to be done.”

Relevant congressional committees are already notified when drone strikes occur. But it’s unclear how the administration, under Obama’s new transparency pledge, will handle public notifications, particularly when Americans are killed.

The public only knew about the deaths of three Americans by drone strikes through media reports and the fourth when Attorney General Eric Holder disclosed it in a letter to Congress on the eve of the speech.

Under current policy, the official U.S. figures of number of strikes and estimated deaths remain classified.

According to the New America Foundation which maintains a database of the strikes, the CIA and the military have carried out an estimated 416 drone strikes in Pakistan and Yemen, resulting in 3,364 estimated deaths, including militants and civilians. The Associated Press also has reported a drone strike in Somalia in 2012 that killed one.

The think tank compiles its numbers by combining reports in major news media that rely on local officials and eyewitness accounts.

Strikes in Pakistan spiked in 2010 under Obama to 122, but the number has dropped to 12 so far this year. Strikes were originally carried out with permission of the Pakistani government of Pervez Musharraf, though subsequent Pakistani governments have demanded strikes cease.

The CIA and the military have carried out some 69 strikes in Yemen, with the Yemeni government’s permission.